The present disclosure relates to acoustic antennas for projection and sensing applications. It finds particular application in conjunction with a leaky wave antenna (LWA), also known as an acoustic prism, in an underwater environment, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
Multi-element linear, also called phased, arrays of transducer elements, like those used in ultrasonic imaging devices, may have high processing bandwidth (typically greater than 100 GHz) requirements, and require high power and complex processing capabilities. LWAs generally utilize a single acoustic source in combination with apertures, replacing the need for an array of sources/sensors. The use of a LWA significantly reduces power requirements when compared to prior art array devices. However, while LWAs are known in the art, they are almost always limited to an air environment due to the acoustically rigid boundaries between the LWA waveguide material and surrounding air and when introduced in a water environment the waveguide walls appear acoustically elastic.
In general, LWA have a single active element at one end of the waveguide and includes periodically spaced slits also called shunts. Radiated power leaks out of the shunts at an angle coupled to the input frequency as the wave travels down the waveguide.
A water environment, having a much higher density and bulk modulus, presents a challenge for LWAs. Specifically, the acoustical impedance of water is approximately 5000 times that of air. Thus, the impedance of the radiating medium (water) is similar to that of conventional LWA waveguide walls. The similarity makes the walls appear acoustically non-rigid (elastic) to the radiating medium. The acoustic elasticity allows for the undesired leakage of sound and results in poor performance of a LWA. The acoustically non-rigid walls may lead to uncontrollable coupling into elastic wall polarizations.
It is desirable to provide a single antenna to replace sensor arrays for use in a fluid environment that accounts for the impedance of the fluid medium and mitigates the elastic waves in the wall and controls leakage.